As you move up the group, the number of electrons means that the atomic radius of the atom

As you move up a group (or column) in the periodic table, the number of energy levels (shells) decreases. This means that the electrons are closer to the nucleus and the atomic radius (the size of the atom) decreases.

This is because the number of protons in the nucleus increases as you move up a group, which increases the positive charge of the nucleus and pulls the electrons closer. At the same time, the number of energy levels decreases, so the electrons are in closer proximity to the nucleus. Therefore, the atomic radius decreases as you move up a group in the periodic table.